The concentration of analytes in whole blood, meaning the combined cellular and fluid portion of blood, may differ significantly in amount from the concentration of analytes found within red blood cells. For example, in whole blood, potassium levels are usually about 4.0 mM, while potassium concentration with in red blood cells is usually about 150 mM.
In the course of collecting and handling whole blood from a patient, some cells, red blood cells in particular, may be physically damaged causing rupture of the red blood cell. The phenomenon of ruptured red blood cells is known as “hemolysis”. When hemolysis occurs in a whole blood sample, the contents of the red blood cells is intermixed with the contents of the cell-free portion of whole blood, termed plasma, or in some cases, serum. Hemoglobin, a constituent of whole blood normally found within red blood cells and not free in the fluid portion of blood, and other intracellular elements, e.g., potassium are released from the intracellular compartment of red blood cells into the fluid portion of blood, i.e. plasma or serum.
Because the concentration of potassium within red blood cells is 25-75 times higher than the concentration of potassium in normal plasma, measuring potassium in the fluid portion of a patient's hemolyzed blood sample will induce an artifact, such as an artificial measured elevation of the patient's actual plasma potassium level. The potassium concentration in the fluid portion of non-hemolyzed blood is an important indicator of numerous conditions. An over estimate of the concentration of potassium in hemolyzed blood may result in treatment of the patient for hyperkalemia (increased blood potassium) when the patient may actually have low concentration of potassium in the patient's non-hemolyzed blood sample. Unfortunately, only a relatively small number of ruptured red blood cells can result in an artificially elevated blood potassium level.
In addition to elevated plasma potassium when a blood sample is hemolyzed, other analytes such as lactate dehydrogenase, acid phosphatase, aspartate aminotransferase, and alanine aminotransferase, for example, are also present in higher concentration in red blood cells than in the fluid portion of blood, and these analytes may be artificially elevated in hemolyzed blood.
Current methods for detecting hemolysis in a patient's blood sample include centrifuging the blood sample to remove blood cells, then by optical methods, determining the presence of hemoglobin in the plasma portion. Hemoglobin imparts a pink or red color to plasma when the color ordinarily in a non-hemolyzed blood sample is slightly yellow. No current methods operate on whole, non filtered or non-centrifuged blood to determine hemolysis.